The invention relates to self-refrigerating devices employing evaporation/condensation processes. Specifically the invention relates to methods for the preparation of heat sink materials useful in such devices, and the heat sink materials resulting from these preparation methods.
Self-refrigerating devices are known in the art. These devices are designed to provide cooling without resort to external sources of cooling such as electricity, ice and the like. These devices can also be designed to be highly portable. Conveniently, they are designed to deliver cooling on a single-use basis, and are therefore disposable.
Many products, including liquid products, have more favorable properties when cold than when at ambient temperatures. Thus, cooling of these products to temperatures of between about 0° C. and 20° C. is desirable. Generally, such cooling is carried out by electrically-powered refrigeration units, or by means of a phase change material such as ice. The use of these units to cool such foods and beverages is not always practical because refrigerators generally require a source of electricity, they are not usually portable, and they do not cool the food or beverage quickly.
An alternate method for providing a cooled material on demand is to use portable insulated containers. However, these containers function merely to maintain the previous temperature of the food or beverage placed inside them, or they require the use of ice cubes to provide the desired cooling effect. When used in conjunction with ice, insulated containers are much more bulky and heavy than the food or beverage. Moreover, in many locations, ice may not be readily available when the cooling action is required.
Ice cubes have also been used independently to cool food or beverages rapidly. However, use of ice independently for cooling is often undesirable because ice may be stored only for limited periods above 0° C. Moreover, ice may not be available when the cooling action is desired.
In addition to food and beverage cooling, there are a number of other applications for which a portable cooling device is extremely desirable. These include medical applications, including cooling of tissues or organs; preparation of cold compresses and cryogenic destruction of tissues as part of surgical procedures; industrial applications, including production of cold water or other liquids upon demand; preservation of biological specimens; cooling of protective clothing; and cosmetic applications. A portable cooling apparatus could have widespread utility in all these areas.
Most attempts to build a self-contained miniaturized cooling device have depended on the use of a refrigerant liquid stored at a pressure above atmospheric pressure, so that the refrigerant vapor could be released directly to the atmosphere. Unfortunately, many available refrigerant liquids for such a system are either flammable, toxic, harmful to the environment, or exist in liquid form at such high pressures that they represent an explosion hazard in quantities suitable for the intended purpose. Conversely, other available refrigerant liquids acceptable for discharge into the atmosphere (such as carbon dioxide) have relatively low heat capacities and latent heats of vaporization. As a result, some cooling devices which release carbon dioxide are more bulky than is commercially acceptable for a portable device.
An alternate procedure for providing a cooling effect in a portable device is to absorb or adsorb the refrigerant vapor in a chamber separate from the chamber in which the evaporation takes place. In such a system, the refrigerant liquid boils under reduced pressure in a sealed chamber and absorbs heat from its surroundings. The vapor generated from the boiling liquid is continuously removed from the first chamber and discharged into a second chamber containing a desiccant or sorbent that absorbs the vapor.